What makes fantasy, fantasy? Is it magic? Is it the low-tech level? The inclusion of creatures from mythological and folkloric sources? What makes a fantasy novel not a science fiction or horror novel?
Someone once told me that one of my stories couldn't be fantasy because it lacked an overt magical element. But there are plenty of low magic backgrounds out there, and they're still fantasy. Most fantasy does include other species or creatures, but not all. I've read stories without dragons, elves, fairies, trolls or anything except humans. They're still fantasy.
Low-technology is common, but there are plenty with higher tech and some that are labeled as a cross between science fiction and fantasy, but they're still fantasy, too. Otherwise, they'd just be called science fiction. :D
I think it's the tropes that make fantasy, fantasy. Tropes are commonly used devices of plot, setting, species or character. The things you expect (or wouldn't be surprised) to see when you read a book in a given genre. Tropes are part of a genre's tradition, built upon with each new generation of writers as they expand (or don't) the genre. Not every book has to be expansive, and there's nothing wrong with not expanding a genre, but there are some books that make it big with the genre's fans. Those books effect the tropes. They reinforce it or subvert it or change it so it's not quite what is was, but not quite something different, either.
For examples of tropes, just visit TVtropes.Org (they cover books, comics and movies, too), but I warn you that you can get lost in that labyrinth and not find your way out for hours! Take a ball of string with you.
Tropes are used over and over again and can be anything from the power of love's first kiss to the hero's journey to the evil (TM) overlord. These are elements that most people aren't going to be surprised to see when they crack the spine of a fantasy novel. Some people are surprised if they don't see the bigger ones.
And, yes, these tropes can get stale. They can become old and brittle and crack apart in your hands. They can become overused and (duh, duh, DUM!) cliché. Oh, most dreaded of labels. For many writers, it's an arrow to the heart. But does it need to be? Do we need to be so worried about clichés?
Well, I think it really depends on what you're trying to accomplish. If you want a reader to put down your book, blink and think "Wow. That was breathtakingly original." Then yes. Yes, you should be terrified of clichés.
But, if what you want is for a reader to put down your book and grin and think "Wow. That was a good read!" Then no. While piling on too many un-subverted or unspun tropes (or full-blown clichés) probably won't make for a good read (the audience already knows where everything is going, after all), a few tropes sprinkled in among your other ideas can actually make a book more relatable to the reader.
They're tools that can help to simplify what could be a complex subject. Complex subjects require explanation, words, and time in order to be related to the reader. The more original complex subjects you have, the less you need one more, especially if it's not original at its heart.
And, while we always want to highlight what's original and unique about our stories, readers are looking for something. Most often, it's something they found in another book. If they're fans of the genre, they're looking for things they found in other fantasy books. And if it's been in enough books to keep them as fans of the genre, it's probably at least a trope.
What's your view on clichés? Do you use them? How do you make yours feel fresh or new? When does a trope become a cliché?